Iodinated contrast media which are injected within blood vessels and CSF cavities still cause neurological complications. The inner mechanism of neural damage is, apparently, a disruption of the blood- brain barrier and/or the blood-CSF barrier. Using the monkey's spinal cord as a model, we are investigating the neural damage caused by radiographic contrast media, its earliest stage of appearance, and its reversibility-irreversibility. Particular emphasis is placed on electron-microscopic appraisal of what is considered the morphologic counterpart of the blood-brain barrier (tight junctions).